The present invention pertains to fuel circuits for internal combustion engines and is particularly concerned with an improvement in a fuel circuit for an internal combustion engine having an electric motor driven control pump which in conjunction with a fuel flowmeter delivers precision-metered fuel to the engine for mixture with induction air to establish a desired fuel-air ratio.
Examples of fuel metering systems with which the present invention may be utilized are disclosed in U.S. Pat. No. 3,935,851 dated Feb. 3, 1976 and pending application Ser. No. 599,243 filed July 24, 1975, now U.S. Pat. No. 4,048,964, both assigned to the same assignee as the present application. In that patent and application there are disclosed novel fuel metering systems wherein an electric motor driven control pump supplies fuel through a fuel delivery circuit to the induction system of the engine for mixture with air ingested by the engine. The fuel delivered to the engine is measured by means of a fuel flow transducer. Induction air flow is also measured. The speed of the motor is controlled by means of electronic control circuitry such that for any given measured airflow over the operating range of the engine the motor speed is controlled to cause a precise amount of fuel to be delivered through the delivery circuit to the engine whereby a desired fuel-air ratio is secured. The system operates in a closed-loop fashion because the actual fuel delivery is measured and the motor speed is regulated to insure that the desired amount of fuel is actually being delivered through the fuel delivery circuit for various operating conditions and changes in various ambient parameters.
In order to achieve best performance it has now been found desirable to have the pump and motor highly responsive to changes in engine operation and/or ambient parameters so that driveability and fuel economy can be improved while products of emissions are correspondingly minimized. In quest of such a responsive system however, it becomes important to avoid oversizing components of the system, particularly the electric motor and control pump, so that unwarranted expenses are avoided and so that minimum electrical energy is consumed by the electric motor in driving the pump. One specific area where improvement is desirable is in the context of improving engine idle quality. It is important that a reasonably consistent flow of fuel to the engine should occur to avoid roughness at idle. At idle the electric motor will be operating at the lower extreme of its speed range. However, when the control pump and motor operate at low speed, friction has been seen to cause a once-per-revolution speed variation which is adverse to performance. Furthermore, when the engine is accelerated from idle, the fuel demand suddenly increases. Under this latter condition it is important that the motor and pump respond quickly to deliver the increased amount of fuel which is suddenly demanded by the engine.
The present invention is concerned with providing an improvement in a system of the foregoing type wherein the motor and pump are caused to operate at a higher speed at engine idle than required to satisfy engine idle speed fuel demand. In this way the adverse effect of once-per-revolution friction speed variation is greatly reduced, a more consistent quality of idle fuel flow is attained, and the system is more capable of responding to accelerations from idle which create a sudden increased fuel demand. Particularly the improvement relates to the provision of a return circuit from the outlet of the pump to the tank and in the preferred embodiments relates to the provision of valve structure disposed in the return circuit which by-passes back to the tank a larger percentage of the fuel output of the pump at idle than at higher engine fuel demands. In one embodiment utilizing a shut-off type valve, this means that the pump and motor do not have to be oversized to accommodate the maximum engine fuel demand and this is important in avoiding unwarranted expense in the system and in minimizing consumption of electrical energy by the motor. By minimizing electrical consumption, related electrical components in an engine-powered vehicle, such as the alternator and battery, can be kept to minimize size.
The foregoing features, advantages and benefits of the invention will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawings.